1. Field of the Invention
The present invention relates to an optical film having a polarizer and at least three phase-difference films laminated thereon.
2. Background Art
A liquid-crystal display device of so-called TN mode, where liquid crystal having a positive dielectric anisotropy is twisted and horizontally aligned between mutually-opposing substrates, has hitherto been primarily used as the liquid-crystal display device. However, even when an attempt is made to display black in the TN mode, birefringence is induced by liquid crystal molecules in the vicinity of the substrates because of a driving characteristic of the liquid-crystal display device. As a result, leakage of light arises, to thereby pose difficulty in displaying perfect black. In contrast, in a liquid-crystal display device of IPS mode, liquid crystal molecules exhibit, in an inoperative state, homogeneous alignment where liquid-crystal molecules become essentially parallel to the surface of the substrate. Hence, light passes through a plane of polarization of the liquid-crystal layer without involvement of substantial alteration. Consequently, in an inoperative state, essentially-perfect black can be displayed by means of placing polarizing plates on upper and lower surfaces of the respective substrates.
In the IPS mode, essentially-perfect black can be displayed in the direction of the normal to a display surface. However, when the display surface is observed from a direction deviating from the direction of the normal, leakage of light, which cannot be avoided for reasons of the characteristic of the polarizing plate, arises in directions deviating from the direction of the optical axis of each of the polarizing plates between which the liquid-crystal cell is sandwiched. Consequently, there arises a problem of the angle of view (hereinafter called a “view angle”) becoming narrow.
An optical film solving this problem is described in JP-A-2005-99476. However, this optical film can suppress leakage of light attributable to the view angle, but encounters difficulty in suppressing occurrence of changes in tint ascribable to the view field.